Omni-directional electro-acoustic converter of electro-magnetic type



March 21, 1961 SABURO UCHIDA 2,976,373

OMNI-DIRECTIONAL ELECTRO-ACOUSTIC CONVERTER OF ELECTRO-MAGNETIC TYPE Filed Oct. 23, 1956 jg dn OMNI-DIRECTIONAL ELECTRO-ACOUSTIC CON- VERTER OF ELECTED-MAGNETIC TYPE Saburo Uchida, Bunkyo-ku, Tokyo-to, Japamassignor to Fukuin Denka Kabushiki Kaisha (known as Fukuin Electric Works, Ltd.), Tokyo-t0, Japan, a Japanese limited-liability company Filed Oct. 23, 1956, Ser. No. 617,879

Claims priority, application Japan Jan. 18, 1956 Claims. (Cl. 179115.5)

This invention relates to an omni-directional electroacoustic converter of the electro-magnetic type, and particularly to an omni-directional electro-magnetic speaker or microphone.

In the usual moving-coil type electric speaker for highpitch sound the sound reproduction is very favorable within a definite frequency band, but it, is very difficult to reproduce very high pitch sound in the higher frequencies of the audible frequency range.

On' the other hand, referring to sound distribution in the electric speaker, it is most desirable that the sound emitted from the speaker be uniformly distributed in all directions. 'In the usual electric speaker, sound emission is unavoidably concentrated upon the ,front surface of the speaker.- The directional character of an electric speaker is generally determined by the dimensions of the effective vibration, surface and the wave length of the sound waves. When the dimension of the vibration surface is too small in comparison with the wave length of the emission wave, the sound directional qualities 'of the speaker becomes similar to that of a so-called double sound source. However, when the. wave length of the oscillation wave is equal to or smaller than the dimension of the vibration surface, the sound field is concen-. trated at the front of the speaker. When the sound wave length is sufiiciently shorter than the dimension of the vibration surface, sound directivity becomes very sharp. The sound directional character of a speaker therefore can be determined by altering the dimension of the vibration surface.

An important consideration in relation to the frequency response character of a speaker adapted to high-pitch sound is whether the speaker can rapidly accommodate to the variations of signal intensity and frequency. A linear or flat frequency response characteristic or range often determines whether the input wave form will coincide with the output sound wave form so as to emit undistorted sound. It is important for the fidelity of a speaker is determined by its frequency response characteristics and range.

A principal object of this invention is to provide a reproducer usable as an improved electric speaker or microphone having a completely omni-directional character and an ability for reproducing high audio frequencies.

A feature of the device according to the invention is that it can function as a speaker which consists of a magnet, magnetic yokes which are so combined with the magnet so as to create a circular magnetic field. A ribhon-shaped moving coil is arranged in the circular magnetic field. A supporter divides the coil into a plurality of elements so as to make the elements of the coil resonate to low and high audio frequencies. Circular, arcuate horns are attached to the circumference of said coil.

The vibratory part of the sound converter or reproducer of this invention is a ringeshaped ribbon conductor forming a vibration surface of which the mass is very small so that its frequency response character can be .ribbon conductor and the circumferential horn.

2 easily determined by a suitable selection of the natural or resonant frequencies of the divided elements of the It is possible to obtain a sufiicient mean sound pressure level within a frequency range from 4000 cycles per second to 20,000 cycles per second by use of the reproducer of this invention. 7

The sound source is omni-directional, over a full 360, because the oscillation system in the circular magnetic field is formed by many coil elements which in turn are arranged in a circular arrangement. Hence, the sound field generated has uniform directional qualities in connection with various frequency bands. In the speaker of this invention, the emission system has a linear frequency response-characteristic over the entire range of high and low audio frequencies. In this way, the output sound wave corresponds to that of the input voltage and a very excellent sound field of high-quality can be obtained so that the fidelity of reproduction is excellent.

The novel features'of this invention are set forth in detail in the appended claims. The construction and operation of the speaker of this invention together with other objects and advantages may be best understood with the aid of the following description and the accompany- V 1; 1

' in Fig. l, in which the magnetic yokes and the horns supported thereby are removed at the upper'half to illustrate the arrangement of the coil,

Fig. 3 is a plan view of a terminal plate in Fig. 2, Fig. 4 is a side view of the terminal plate shown in Fig. 3.

' In Figs. 1 and 2, a cylindrical permanent magnet 1 is supported by two plate-shaped magnetic yokes 2 and 2a having ring-shaped poles lllfand l0aywhich face each other spaced by a small airgap G. A support ring 3, is concentrically arranged aroundthe magnet 1. This ring has many projections 5 angularly spaced and distributed around-it. A-ribbon-shaped'movingcoil 4 made of a light alloy toll is supported on the projections 5. A horn 6is attached to the yoke 2 and anothehhor-nfia is attached to the yoke'2a. Both horns 6 and 6a have an open sector I or gap 11 and face in opposite directions from each other. At gap 11, the moving coil 4 is supported by resilient members 7 While terminals 8 of said coil are supported I by an insulating terminal plate 9 which in turn is fixed to the support 3.

According to the construction as described above, the

following results are obtained:

(A) A ribbon-shaped moving coil 4 1s circularly arranged as the sound emission surf-ace in a strong magnetic field, so that when the lengths of the elements into i which said coil is divided'are suitably selected all resonance frequencies from the lowest audio frequency to the highest are faithfully reproduced. That is to say,

the speaker of said type is uniformly responsive over all frequencies from the lowest up to 20,000 cycles per sec end.

(B) Due to a circular arrangement of the oscillation elements or vibratory surfaces a sound field is obtained in all directions;

(C) The moving coil consists of a ribbon-shapedfoil having a relatively low mass, so that its efficiency isvery high.

characteristics are excellent.

Patented Mar. 21, 1961 (E) Although the ribbon-shaped moving coil conductor is thin and flexible, the current is uniformly distributed in it. The conductor is then oscillated in the strong magnetic field so that it can create all of the sound pressures without being distorted by air pressure.

(F) The moving coil is stretched and supported by resilient members, so that it is very stable against distortion of the coil metal and the effects of temperature.

The converter or reproducer of this invention may be used not only as a speaker, but also as an omni-directional microphone which it is constructed as a small unit. When it is to be constructed as a presure-type omni-directional microphone, it is only necessary to make it so that the resistance thereof is varied by changes in air pressure by closing the ends of the coil conductor. However, when it is to be constructed as a dynamic omni-directional microphone, it is only necessary to construct it such that air passage over surface of the coil conductor is possible.

It is possible to make a perfectly omni-directional microphone, which is an entirely new and novel feature of the arrangement.

While I have illustrated particular embodiments of my invention, it will be understood, of course, that I do not wish to be limited thereto, since modifications may conceivably be made. I propose therefore by the appended claims, to cover all such modifications as may fall within the true spirit and scope of this invention.

I claim,

1. An omnidirectional device of the electrodynarnic type for converting sound into electrical energy comprising, means including a cylindrical permanent magnet for establishing a magnetic field,.a continuous flexible conductor disposed spaced from and circumferentially of said magnet and in said magnetic field, means dividing the conductor into a plurality of portions each capable of vibrating freely in said magnetic field in response to pressure waves of a sound field to generate electrical energy in said conductor in response to the sound field, and means connected to the conductor for receiving an electrical output therefrom.

2. An omni-directional device of the electrodynamic type for converting sound into electrical energy comprising, means for establishing a magnetic field, a continuous flexible ribbon conductor disposed in said magnetic field, means dividing the ribbon conductor into a plurality of portions each capable of vibrating freely in said magnetic field in response to pressure waves of a t sound field to generate electrical energy in said conductor in response to the sound field, and acoustic directional means cooperating with said conductor and disposed coaxially therewith for directing sound-pressure waves in opposite directions.

3. An omni-directional device of the electrodynamic type usable for converting electrical impulses into sound and alternatively usable for converting sound into electrical impulses comprising, means for establishing a substantially circular magnetic field, a continuous flexible ribbon conductor disposed in said magnetic field, and means dividing the ribbon conductor into a plurality of circularly arranged portions each capable of vibrating freely in said magnetic field to generate electrical energy in response to a sound field and each being frequency-responsive to alternative application of electrical impulses thereby to generate a substantially uniform sound field in all directions.

4. An omni-directional device of the electrodynamic type for converting electrical impulses into sound comprising, means for establishing a magnetic field, a continuous circularly arranged flexible ribbon conductor, means dividing the ribbon conductor into a plurality of portions each capable of vibrating freely and independently in said magnetic field and arranged to resonate in response to the application of electrical impulses to the conductor to generate a sound field in response to said electrical impulses, and means for applying electrical impulses as an input to the conductor.

5. An omni-directional device of the electrodynamic type for converting electrical impulses into sound comprising, means for establishing a magnetic field, a continuous flexible strip conductor disposed substantially in a circle, means comprising a circular member having a plurality of peripheral spaced projections and substantially around the periphery of which the conductor is disposed dividing the strip conductor into a plurality of portions each capable of vibrating freely in said magnetic field, and arranged to resonate in response to the application of electrical impulses to the conductor to generate a sound field in response to said electrical impulses, resilient means for tensioning the conductor along its longitudinal dimension and holding the conductor spanning the spaces between said projections, and means for applying electrical impulses as an input to the conductor.

No references cited. 

